1. Field of the Invention
This invention relates generally to the field of magnetic devices and more particularly to a magnetic circuit including a structure for magnetically cladding a permanent magnet to eliminate undesirable external magnetic fields.
2. Description of the Prior Art
Various magnetic devices generating a controlled magnetic field are known to include magnetic cladding to enhance the desired controlled magnetic field as well as to reduce the external affects of the magnetic circuit on the surrounding environment due to magnetic field leakage. Various applications include, for example, electron beam devices such as klystrons, traveling wave tubes and the like, as well as nuclear magnetic resonance imaging systems.
Two examples of such devices include the teachings of U.S. Pat. No. 3,768,054, entitled, "Low Flux Leakage Magnetic Construction" issued to Wendell Neugebauer, on Oct. 23, 1973, and U.S. Pat. No. 4,647,887, entitled, "Lightweight Cladding For Magnetic Circuits", issued to H.A. Leupold, the present inventor, on Mar. 3, 1987. In both instances, magnetic flux of a first magnet is conserved by placing a second permanent magnet externally adjacent the first magnet with the magnetic fields of the second magnet perpendicular to the axis of the first magnet in order to prevent leakage of flux from the first magnet. As a result, most of the flux generated by the first magnet in directions outwardly from the main axis is redirected inwardly to increase the magnetic intensity along the main axis. Although the prior art devices such as disclosed in the Neugebauer and the Leupold patents, they inherently include structures which provide undesired levels of flux leakage for certain applications in the vicinity of their ends.